Newly registered users with Jetpack SSO aren't fully connected

#### Steps to reproduce the issue

1. In Settings->General, check "Anyone can register"
2. Enable the Jetpack SSO module
3. In an incognito window, go to yousite.com/wp-login.php
4. Log in via SSO (which should auto-create the user account)

#### What I expected

Fully authenticated - connecting via SSO should really make me "fully connected".

#### What happened instead

System seems to think I have not connected my account to WPCOM.

**Screenshots**

Start by reproducing the issue with “Anyone can register” enabled and Jetpack SSO active, then trace the SSO login and auto-created user flow. Compare the resulting connection state with an already connected account; done means a newly registered SSO user is recognized as fully connected to WPCOM.

Written by the indexing model from the issue text.